A vehicle with an engine may include an evaporative emission control system coupled to a fuel system in order to reduce fuel vapor emissions. For example, an evaporative emission control system may include a fuel vapor canister coupled to a fuel tank which includes a fuel vapor adsorbent for capturing fuel vapors from the fuel tank while providing ventilation of the fuel tank to the atmosphere.
Leak testing may be periodically performed on such evaporative emission control systems in order to identify leaks in the system so that maintenance may be performed and mitigating actions may be taken in order to reduce emissions. In some approaches, leak testing may be performed using active leak testing systems which include various components such as one or more pumps. For example, an evaporative leak testing module (ELCM) may be included in a vehicle to determine leak testing based on a reference orifice size.
The inventors herein have recognized that such approaches to leak testing may not be capable of detecting leaks with a size less than a threshold size, e.g. such systems may not be capable of detecting 0.010″ orifice leaks due to limitations of components in the leak detection system. For example, an ELCM may only be able to detect leaks with an orifice size greater than or equal to 0.020″. The inability of leak detection systems to detect such small leaks may lead to increased emissions and potential degradation of engine operation due to undetected leaks.
In order to at least partially address these issues, methods for diagnosing leaks in an engine with an evaporative emission control system are provided. In one example approach, a method comprises, during an engine-on condition, delivering fuel from a fuel tank to one or more cylinders of the engine while the fuel tank is sealed off from atmosphere, and indicating a leak based on pressure in the fuel tank. For example, a leak may be indicated in response to a pressure decrease in the fuel tank greater than an expected pressure decrease, where the expected pressure decrease is based on a fuel level in the fuel tank.
In this way, leak detection for very small leaks, e.g., leaks with a size less than a threshold detectable by leak diagnostic components such as an ELCM, may be performed. Further, in such an approach leak detection may be performed without additional components such as additional pumps, fuel reservoirs, leak check modules, etc., thereby potentially reducing costs associated with additional leak diagnostic components. Further, in some examples, such an approach may be used in addition to other leak diagnostic approaches to increase accuracy of leak testing and/or as an initial screening, e.g., to determine if a potential leak is present before performing an active leak test which consumes power.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.